Gas purification



April 5, 1932. c. .1. HANSEN 1,852,160

GAS PURIFICATION original Filed Aug-2o, 1928 y MM' Affy.

` great disadvantage that in the case where iron Patented Apr. 5, 1932 UNITED STAT-Es PATENT orties CHRISTIAN' J'. HANSEN, 0F ESSEN-RUHR, GERMANY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO THE KOPPERS COMPANY, OF PITTSBURGH, PENNSYLVANIA, A COR- tPonArroN or DELAWARE GAS PURIFICATION Original application filed August 20, 1928, Serial No. 300,945, and in Germany October 22, 1927. Divided q and this application filed December 4, 1929. `Serial No. 411,685.

. ve-ntion to provide means whereby the animonia .and sulfur which are contained in such gases, the latter mostlyunder the form of hydrogen sulfide, can be recovered from the gases in an easier and more perfect manner .than was hitherto possible.

It is Vknown to recover the ammonia and hydrogen sulfide from gases bymeans of solutions of metal thionat-es. In this process there results metal sulfide and a solution of ammonium thionate and in some cases also free sulfur.

The Vmetal sulfide, which may be ferrie sulfide, manganese sulfide or zinc sulfide is reh dissolved by acting thereon with sulfur dil`oxide and there results a metal thionate solu- 'tion and free sulfur. rThis solution has hitherto been treated further in such manner that the solution containing, besides sulfur, metal.

and ammonium thionates in solution, was de* composedby heating into sulfate and sulfur, vand the metal (iron, manganese or zinc) was removed by treating the sulfate solution with fresh gas before starting the gas purification Y process proper.

The process above described involves the is present, iron disulfide (FeSZ) is obtained', which is not soluble in sulfur dioxide and other acids.

VThe metal thionate solutions described are l further able only to take up ammonia andhydrogen sulfide in the predetermined proportion of 2NH3r1H2S. Now in view of the fact that the gases result-ing for instance 1n the distillation of coal always contain more hydrogen sulfide (gas resulting in the distil lation of Ruhr coal about 50 per cent, English coal partly l() to 200 per cent more than corresponds to the above proportion), a proc- .ess of purification as above described always leaves a more or less considerable proportion of hydrogen sulfide in the gas. Y

It is further known to remove hydrogen sulfide from gases free from ammonia by dif-v .4 `ferent' means such `as -V l reaction of these solutions is always so small that inthe case of a polythionate solution and a gas containing for instance 0,8 per cent HgS, only 38 per cent of the hydrogen sulfide can be removed, with a solution of thiosulfate and .sulfur dioxide only about per unitof time.

'.On theother hand a suspension of ferric hydroxide will act on a gas washing liquor having neutral or slightly alkaline reaction so favorably that the total removal of hydrogen sulfide can be effected under commercial conditions.

Unfortunately the use of suspensions of ferrie hydroxide involves the great disadvantage, that when thespent washing liquor is regenerated with air or another gas containing oxygen, there results a mixture of ferrie .hydroxide and sulfur and the separation of Vthe sulfur from the iron sludge is very ex- -pensive. One is further forced to keep'the percentage of iron in such solutions'as low aspossible in order to obtain the most favorable proportion between the sulfurrand the iron. This entails the drawback, that the absorbing capacity of such washing liquor for hydrogen sulfide is comparatively small.

With an iron content of about 2 kes. per cubic meter of the solution, not more than 100 cubicmeter gas can be treated at the utmost.

in my copending application for patent of the United States, Serial Number 300,945.,

l have described a method of treating coke oven gases for the recovery therefrom of useful admixtures, which allows obviat-ing the drawbacks inherent in both absorption modes 4by carrying them out in succession. It congen sulfide and ammonia are absorbed.

This methodv allows removing, besides the ammonia. contents, all the hydrogen sulfide from a gas irrespective of the ratio of the contents of these two admixtures and more particularly from a gas which containseven less than QNH3 per 1H2S. On the otherV hand the elementary sulfur obtained can readily be recovered in a pure state free of ferrie or manganese hydroxide by mixing the two different washing liquors when spent,

dividing the mixtures into two arts and separately `regenerating each part by treating it with air or sulfur dioxide, respectively. While the suspension of free sulfur and fer-ric or manganese hydroxide obtainedby blowing with air is immediately reused, the liquor obtained by the introduction of sulfur dioxide which contains iron or manganese thionates in solution and elementary sulfur in suspension, is first filtered, whereby the sulfur is ob;- tained in a pure state free of ferrie or man ganese hydroxide. y

This method, which is applicable irrespective of whether the so-called direct, semidirect or indirect way of separating the bulk of the ammonia is used, renders it necessary toemploy and to control at least two different washing stages. It can be simplified in accordance with the present invention by washing the gas with a single washing liquor, which contains iron or manganese hydroxide in suspension and thionates of one or both of such metals in solution. lf the gas is brought in contact with such combinedwashing liquor, it will absorb from the gas ammonia and hydrogen sulfide in any desired ratio, the iron or manganese thionate combining with the total contents of ammonia and one-half of the equivalent quantity of hydrogen sulfide,

. dioxide, while the other is treated with air to produce ferric hydroxide. The regenerated suspension of ferric or manganese hydroxide and the regenerated solution of thionates, from which free sulfurmay be filtered off, are then mixed and returned into the washing apparatus.

It willbe understood A,that free sulfur is formedin the new process in various waysY during the washing stage as well as in the two regeneration stages. In the washing liquor ferric hydroxide reacts with hydrogen sulfide according to the equation:

2Fe(OH) 3+8H2S=2FeStS+6H2O (l) Ferric or manganese polythionates contained in the washing liquor react with hydrogen sulfide in the presence of ammoniaindifferent ways, whereby free sulfur is formed, for instance by the following .re-

action FeSiOSJfn-ns JVQNHS: Y

When regenerating part of the spent washing liquor with air sulfur is obtained by the reaction ,The other portion of the spent liquor, whenVV regenerated bymeans ofy sulfur dioxide, yields another quantity of free sulfur according'to reactions of the following types:

present in the form of dissolved thionates.- it will further be understood, that this recovery, or filtering off, of sulfur immediately after the mentioned regeneration step, yields not only the amounts of sulfur which are formed during this one step, but involves alsoV the recovery of part of the quantities of sulfur formed in the other regeneration step as well as 1n the washing step proper, as allV these liquors are later on partlysubjected to the regeneration by means of sulfur dioxide.

It has already been suggested to recover hydrogensulfide and ammonia from coal distillation gases by washing same with a liquor containing sulfides and thionates of iron, zinc` or manganese, whereby this liquor is alternately or simultaneously regenerated by introducing sulfur dioxide. Only when starting this process a suspension of the hydroxides of these metals is used, which are soon converted into the sulfides and their derivatives. In contradistinction therefrom my invention is limitedY to the step of maintaining in the washing liquor a contents of unconverted metal hydroxide substantially f throughout the washing period,rthe formed metal sulfide being preferably regenerated by treating part of the spent washing liquor with air or other gas mixtures containing oxygen.

When producing ferric hydroxide in Ythe` spent washing liquor by treating same with air, it is astonishing to find that the oxidation which may amount tot() percent and. more;

nosuch process'has hitherto been suggested. 'A particular. technical. advantage of Athe new mode of operating consists'therein,;that `it can easily be adapted'to widely: differing conditions of operation andto y,all kindsyof ously and recover the ammonium salts `contained therein in any suitable way, for in-V stance by filtering olf sulfur and metal sulfide Vfrom part of the spent liquor, and heating the liquor from metals at the point before the apparatus.

The purification eifect 4is practically `in- I vdependent from all variations ,in .the composi tionof the gas and inthe production,` more lespecially when different kinds ofgas; are produced. v 4

In the flow sheet and forming part thereof` my,` inventionis -illustrated by way of example.

By the repeated regeneration and recirculation of thewashing liquor used in. my proc ess the contents of ammonium thionatesthere-A of is gradually increased. I` `may. withdraw part' ofthe liquid periodically orfcontinuthe filtrate in order to convert'the thionates into sulfates and free sulfur. If the liquor subjected to this treatment contains some metal thionates, it mustbe `treated later on with hydrogen sulfideand ammonia in order l to precipitate Aand separate the metals vunder the form of sulfldes, whichgcan be reintroduced into the washing cycle. Howeven inA contradistinction to .this hitherto employed method, I prefer inserting the stepk of freeing sulfate is formed, as. only. by, so doing the formation of ferrie disulfides (FeS2) can be prevented, which cannot be dissolvedby tre-atn Y. cyanic acid). per cubicmeter,is washed in ac-v l ment with sulfur dioxide.

Ait any rate the ,precipitated and filtered-r Vjwith a-liquor` containing about l050 kgs. iron o metal sulfides should be reintroduced into the process, preferably by adding them tothat portion-of the spent washing liquor which is to be treated with sulfurdioxide.

My invention at the same time enables me to extract from the gas-also the cyanogen or its compounds contained therein, and to con- `vert same into ammonium thiocyanate, from which can then be obtained ammonium sulfate and sulfur in themannerdescribed in my copending application for Letters Patent of the United States for Improvements in .r treating thiocyanates, Ser. No. 298,617.

In this copending application I have shown that if ammonium thiocyanate is decomposed hydrolytically within the washing liquor,-

which results in the purification of coal distillation gases, such washing `liquor containing either polythionates,v or kcorresponding quantities of thiosulfate and sulfur dioxide l upon this portion is also reused incycle'.

combined therewith, the two being converted into polythionates, or if suchsalts. or sulfur dioxide or both are introducedintothe liquor,

finto two portions.

or if ammonium bisulfite or ammonium sultemperature, more especially under pressure,

preferably at a temperature `varying between 140f160C- .i u y w yAs all the'washing liquors used inthepurifcation of the Ygascontain free vsulfur andas the suspensions of ferrie hydroxide. as. well .as the iron. thionate solutions cany con-tain some ammonia duringthewashing procedureathey aiixed to this speciication'.4

will also absorb from-the gas all cyanogenV compounds, which are convertedinto ammonium I thiocyanate. vWhen treating fthe spent: .washthelgas, being, primarily. formed.`v from the :nitro-gen 1in the coalwhen acted uponbyfthe incandescent coal and the hotproductsfofzdistillation, v,is ,converted into cyanogen Vcompounds. `Thereby hitherto a materialpropor tion of the ammonia, about 10-20% andlmoreV was decomposed. ,The `present process thereforeenables meto obtainl 10-20. per :cent and .more ammonium sulfate in excessV ofthe .quantity Vhitherto obtainable. i

EampZe1.-Acolre ovengas which at a n `temperature abovexits -dew point V,contains aboutS grs. NH3, l2vgrs.H2S and 1,7 grs. cyanogen compounds (calculated as. hydrocordaiice with the method described above per cubicineter partly .in the formA of suspended ferric hydroxide. and partly inthe form of dissolved thionates. The total con- .gencompounds is yextracted by the .washing liquors `which may have an ammoniacalreaction. The` spent liquor contains ironinthe form of` Fe'S and, free sulfur in suspension, and, besides, ammonium" thionatesl and am monum thiocyanate in solution. Itisdivided One portion, preferably one third ofthe total amount, is treated with air, whereby the metal sullides are converted inginsuspension is thenfilteredtoii where- When the liquor has become. rich enough in ammonium salts, I periodicallyor continuf f .1.= 5"1 22.11"" i' ously withdraw part of the spent liquor for the recovery of ammonium sulfate. I treat this portion first vvith an excess of freshgases in order to precipitate all the dissolved metal .compounds under the form of sulfides, Which are filtered oiftogether with free sulfur and reintroduced in the process. The filtrate thus obtained, which chiefly consists of a solution vof ammonium thiosulfate, ammonium thiocyanate and some ammonium polythionates, is then heated under pressure to about 200o C. in a pressure resisting vessel,.as described in my copending application for patent men- Vtioned above. VThe thiocyanate is thereby converted as Well as the thionates vinto ammonium sulfate and sulfur. I thus obtain an increase in the yield of ammonium sulfate formed from the ammonia in the gas, vvhich` 'amounts to 13,4 per cent, the nitrogen contents of the cyanogen compounds being alsol converted into ammonia.

- E mamy-Ze 2.-A gas containing 8 grs. NH3, 12 grs. H25 and.1,7 grs. cyanogen compounds (calculated as HCN) per cubicineter is treat-v ed for instance as described With reference to Example 1. After the Washing liquor is exhausted, the ammonium salt solution is` separated from the ferric sulfide formed either by filtration or by decantation, cen-- trifuging or the like. There is obtained an.

. ammonium 'salt solution containing ammo-- nium' thiosulfate and ammonium thiocyanate in the molecular proportion of 4,24: 1,00, the contents of salt varying Within Wide limits: according to the manner of proceeding and. to the concentration of the ammonia liquor. It is possible to increase the concentration ofv the salts in the solution to about 7 0 per cent.A

If the solution contains forinstance'460 grs. ammonium thiosulfate and 55,8 grs. am-' monium fthiocyanate per liter, 193,4 grs.. sulfur dioxide per 'liter are introduced into` the solution and the liquor thus treated is at. once heated in an autoclave to 140-160o C. or preferably to about 20G-220 C. Theautoclave may either consist of a chrome ample 2, but 257,5 grs. sulfur dioxide arein troduced per liter of the original solution.. If the solution is then .treated as described.

- With reference to Example 2, there are ob tained 10,7 grs. sulfur per liter of theoriginal solution in excess of the'v quantity obtained according toAExample 6. Words instead of 196,6 grs. there are obtained In other 207,3 grs. sulfur, besides which are formed 65,4 grs. free sulfuric acid.

For the purpose of recovering neutral ami nionium` sulfate, Athis acid; solution can be' neutralized before evaporation With ammov nia liquor or the like,or else the ymother liq' uor rich in sulfuric acid, which remains over" when evaporating, can be returned fromftime to time into the decomposition vessel to replace part of the sulfuric acid to be added.

Eamplerd salt solution is treated yas described with reference to Example'2, hovv- -ever the liquor is not heated at once,but is .allowed'to stand sometime after the sulfur dioxide has been introduced. The thiosul- :fate in solution vvill'then begradually converted under the action of the sulfur d ioxvide into poly-thio'nates,in the first line trior 'tetrathionate If the solution is then heated,

which now mainly contains, instead of the thiosulfate and sulfur dioxide, polythionatesY :and ammonium thiocyanate, the heating'being effected as described With reference to `Examples 2 or 3, exactly the same result will be obtained including the same quantities yof ammonium sulfate, sulfur and carbon dioxide as in Example 2.

Example 5.-A solution as described with .reference to Example 3, into'vvhich sulfur dioxide has been introduced, is treated'exactly as described with reference to Example 4, and the same products are obtained as in Example 3.

Example 6.-To a solution as described -with reference to Example 2, are added 997 grs. sulfuric acid of 20 per cent and the .liquor is heated as described with reference- `to Example 2. There are formed 507 grs. ammonium sulfate, 163,9 grs. sulfur and .32,25 grs. carbon dioxide. K

The latter example shows Vthat a mixture of thiosulfate and ammonium thiocyanate can also be decomposed into sulfate'and sulfur vby adding sulfuric acid, and `infconsequence 'thereof the acid solutions ofammonium sulfate obtained according to Examples 3 and .5 can be treated further'in such manner, that `the mother liquors rich in sulfuric acid, 'Which result after evaporation for the recovery of the sulfate, can be utilized for de- 1 composing further quantities of thiosul- Yfate-ammonium thiocyanate solutions. 'Therefore in this case part of the sulfur dioxide used 'according to Examples 2 to 5 tmay be replaced by sulfuric acid, 3 molecules SC2 being replaced by 2 molecules Z'H2SO4.-

bviously the proportions given in the examples need not lto be the same throughout, but all such solutions can be treated for the lrecovery of sulfate and sulfur which contain, ,besides ammonium tliiocyanate, ammonium thio-sulfate, sulfur dioxide, ammonium polythionate and sulfuric acid. Sulfites and A...bisulfites may also be present.

In calculating the composition of such solutions the follovving rules apply:

l. lNHiCNS is decomposed to form sulfate and sulfur by means of:

(a) 2 molecules SO2.

(o) 2 molecules polythionate.

(c) 2 molecules tliiosulfate-l-S molecules (el) 8 molecules bisulte.

(e) 2 molecules thiosulfate-l-2 molecules 2. Thiosulfates, sultes, bisulfites and polythionates are decomposed under the formation of sulfate and sulfur according to the following rules:

(a) 2 molecules thiosulfate-l-l molecule polythionate.

(Z2) 2 molecules sulite-l-l molecule polythionate.

(c) 2 molecules bisulite-I-lmolecule thiosulfate.

(d) 2 molecules bisulfite-l-lmolecule sul- Any of these stocks may be mixed with each other in any desired proportion and in all cases sulfate and sulfur will result. If more sulfite or thiosulfate is present than corresponds to these prescriptions, non-decomposed thiosulfate and, if ammonium thiocyanate is present, also non-decomposed ammonium thiocyanate Will remain in solution.

On the other hand if the solution contains more bisuliite or more polythionate than in dicated above, there'are formed besides sulfate and sulfur more or less free sulfuric acid and, if ammonium thiocyanate is present, also carbon dioxide. In such case, as shown above, the mother liquor rich in sulfuric acid which remains over when evaporating for the recovery of sulfate, is preferably returned into the decomposition vessel.

Various changes may be made in the details disclosed in the foregoing specification Without departing from the invention or sacrificing the advantages thereof.

In the claims the terms metal hydroxide of the iron group77 and metal thionate of the iron group are intended to mean iron and manganese exclusively.

claim:

l. The method of treating coke oven gases for the recovery therefrom of useful admixtures which comprises treating such gas with a solution of a metal thionate of the iron group, in which a metal hydroxide of the iron group is suspended, and maintaining` in the Washing liquor a content of such unconverted hydroxide substantially throughout the Washing period.

2. The method of treating coke oven gases for the recovery therefrom of useful admixtures Which comprises treating such gas vvith a solution of a metal thionate of the iron group, in Which a metal hydroxide of the iron group is suspended, dividing the spent liquor and treating one part With air, the remaining part being treated With sulfur dioxide, re.- moving sulfur from the part thus treated by filtration and remixing the liquors thus treated in a further operation.

3. The method of treating coke oven gases for the recovery therefrom of useful admixtures which comprises treating such gas With a solution of a metal thionate of the iron group, in which a metal hydroxide of the iron group is suspended, the proportion of hydroxide to thionate being substantially l 2, dividing the spent liquors, treating about one-third With air, about two-thirds with sulfur dioxide, removing sulfur from the part thus treated by filtration and remixing the vliquors thus treated in a further operation.

4. The method of treating coke oven gases for the recovery therefrom of useful admixtures which comprises treating such gas with a solution of iron thionate, in which ferric hydroxide is suspended, and maintaining in the Washing liquor a content of such unconverted hydroxide substantially throughout the Washing period.

5. The method of treating coke oven gases for the recoverytherefrom of useful admixtures which comprises treating such gas With a solution of iron thionate, 1n which ferrie hydroxide is suspended, dividing the spent liquor and treating one part With air, the remaining part being treated With sulfur dioxide, removing sulfur from the part thus treated by filtration and remixing the liquors thus treated in a further operation.

6. The method of treating coke oven gases for the recovery therefrom of useful admixtures which comprises treating such gas With a solution of iron thionate, in which ferric hydroxide is suspended, the proportion of hydroxide to thionate being substantially 1:2, dividing the spent liquors, treating about onethird with air, about two-thirds With sulfur dioxide, removing sulfur from the portion treated With sulfur dioxide by filtration and remixing the liquors thus treated in a further operation.

7 The method of removing ammonia and hydrogen sulfide and of recovering useful admixtures from a coke oven gas containing a greater percentage of hydrogen sulfide than corresponds to the proportion 2 mols. NH3: l mol. HZS, comprising treating such gas with a solution of a metal thionate of the iron group, in Which at least as much of a metal hydroxide of the iron group is kept in suspension as is necessary for the absorption of the excess of hydrogen sulphide over said proportion.

n testimony whereof I aflix my signature.

CHRISTIAN J. HANSEN. 

